Animal studies have shown that previous exposure to lipopolysaccharide (LPS) can limit ischemia-reperfusion injury. We tested whether pretreatment with LPS also protects against ischemia-reperfusion injury in humans in vivo. Fourteen volunteers received bolus injections of incremental dosages of LPS on 5 consecutive days (LPS group). Before the first and 1 day after the last LPS administration, the forearm circulation of the non-dominant arm was occluded for 10 min, with concomitant intermittent handgripping to induce transient ischemia. After reperfusion, 0.1 mg of ( 99m)Tc-labeled annexin A5 (400 MBq) was injected intravenously to detect phosphatidylserine expression as an early marker of ischemia-reperfusion injury. Similarly, the control group (n = 10) underwent the ischemic exercise twice, but without pretreatment with LPS. Annexin A5 targeting was expressed as the percentage difference in radioactivity in the thenar muscle between both hands. Endotoxin tolerance developed during 5 consecutive days of LPS administration. Annexin A5 targeting was 12.1 +/- 2.2% and 10.4 +/- 2.1% before LPS treatment at 1 h and 4 h after reperfusion, compared to 12.2 +/- 2.4% and 8.9 +/- 2.1% at 1 h and 4 h after reperfusion on day 5 (P = 1.0 and 0.6, respectively). Also, no significant changes in annexin A5 targeting were found in the control group. So, in this model, LPS-tolerance does not protect against ischemia-reperfusion injury in humans in vivo.